Linear engine and housing for engine

ABSTRACT

A linear engine, comprising a tubular housing, axially spaced electromagnetic coils disposed around the tubular housing, a piston disposed within the tubular housing, the piston including magnetic elements, and a drive circuit electrically connected to the first and second electromagnetic coils for sequentially energizing the first and second electromagnetic coils to reciprocate the piston within the tubular housing. A magnetic sleeve is disposed within each coil, with the piston being arranged to pass through the magnetic sleeves during operation and the magnetic sleeves being separated by nonmagnetic material. The magnetic sleeves each form part of the tubular housing. Sealed bearings at each end of the piston define a sump for retaining lubricating oil within a reduced diameter portion of the piston. The sealed bearings each comprise axially spaced circumferentially extending ribs, adjacent ribs being separated by a gap for receiving a sealing element.

BACKGROUND OF THE INVENTION

[0001] This invention relates particularly to linear engines, that is,motors and pumps of the type that have a reciprocating piston confinedwithin a housing, the piston being driven by a magnetic field generatedby a coil or coils disposed around the housing, as well as otherengines.

[0002] Various linear engines are known, as for example shown in U.S.Pat. No. 4,687,054, 3,910,729, 6,092,999, 6,127,750, 5,083,905,4,509,001, 4,541,787, 4,965,864, 4,692,673, 5,924,975 and EurekaNovember 1997 Article “Shuttling Magnet Ensures Efficient GasCompression.

SUMMARY OF THE INVENTION

[0003] This invention is directed towards a linear engine that, as withthe references cited above, provides a simple, low maintenance, pump ormotor (engine).

[0004] Therefore, according to an aspect of the invention, there isprovided an engine, comprising a tubular housing, axially spacedelectromagnetic coils disposed around the tubular housing, a pistondisposed within the tubular housing, the piston including magneticelements, and a drive circuit electrically connected to the first andsecond electromagnetic coils for sequentially energizing the first andsecond electromagnetic coils to move, as for example reciprocate, thepiston within the tubular housing. In a first aspect of the invention, amagnetic sleeve is disposed within each coil, with the piston beingarranged to pass through the magnetic sleeves during operation and themagnetic sleeves being separated by nonmagnetic material. In a furtheraspect of the invention, the magnetic sleeves each form part of thetubular housing. In a further aspect of the invention, sealed bearingsat each end of the piston define a sump for retaining lubricating oilwithin a reduced diameter portion of the piston. In a further aspect ofthe invention, the sealed bearings each comprise axially spacedcircumferentially extending ribs, adjacent ribs being separated by a gapfor receiving a sealing element.

[0005] These and other aspects of the invention are described in thedetailed description of the invention and claimed in the claims thatfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] There will now be described preferred embodiments of theinvention, with reference to the drawings, by way of illustration onlyand not with the intention of limiting the scope of the invention, inwhich like numerals denote like elements and in which:

[0007]FIG. 1 is a cross-section of a first embodiment of a linear engineaccording to the invention;

[0008]FIG. 2 is a cross-section through an end of a second embodiment ofa linear engine according to the invention;

[0009]FIG. 3 is a cross-section of a third embodiment of a linear engineaccording to the invention;

[0010]FIG. 4 is a perspective exploded view of the embodiment of FIG. 1;

[0011]FIG. 5 is a section through a piston for use with the linearengine of FIG. 1;

[0012]FIGS. 6A, 6B and 6C are sections through alternative embodimentsof the piston of FIG. 5; and

[0013]FIGS. 7A and 7B are perspectives, partly exploded, showing thedesign of alternative sleeves for use in the linear engine of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0014] In this patent document, “comprising” means “including”. Inaddition, a reference to an element by the indefinite article “a” doesnot exclude the possibility that more than one of the element ispresent.

[0015] As shown in FIGS. 1 and 4, a linear engine 10 is formed around atubular housing 12 between a pair of end plates 14, 16 with a centralflange 18. Electromagnetic coils 20, 22 are disposed around the tubularhousing 12, each coil being made for example by winding a wire aroundthe tubular housing 12. The coils 20, 22 are axially spaced from eachother along the housing 12. The size of the gap between the coils 20, 22is variable provided there is an unmagnetized portion between the coils20, 22. A piston 24 is disposed within the tubular housing 12. Thepiston 24 includes magnetic elements, such as by being made of amagnetic material, or by having magnets carried by the piston 24. Adrive circuit 26, incorporating a conventional power supply, iselectrically connected to both electromagnetic coils 20, 22 forsequentially energizing electromagnetic coils 20, 22 to reciprocate thepiston 24 within the tubular housing 12. Drive circuits for such linearmotors are known in the art and need not be further described here indetail. Rods 31, with suitably threaded ends and bolts, not shown, maybe used to secure the housing 12 together, although any of various waysknown in the art could be used to secure the structure together.

[0016] In an embodiment of one of the inventions described in thispatent document, magnetic sleeves 30, 32, for example made of steel, areeach disposed inside a respective electromagnetic coil 20, 22, with thepiston 24 being arranged to pass through the magnetic sleeves 30, 32during operation. The magnetic sleeves 30, 32 are separated from eachother by non-magnetic material, such as a further sleeve 34, which forexample may be ceramic. As shown in FIGS. 1 and 4, the sleeves 30, 32and 34 may be correspondingly stepped for ease of fitting the partstogether. As shown, therefore in FIGS. 1 and 4, the magnetic sleeves 30,32 each form part of the tubular housing 12.

[0017] In a further embodiment shown in FIG. 5, a series ofelectromagnetic coils 50, 52 and 54, with corresponding magnetic sleeves60, 62 and 64 are provided spaced axially along the housing 12, andspaced by non-magnetic sleeves 56, 58, for example made of ceramic. Theremaining components of the linear engine of FIG. 5 are designed in likemanner to the components of FIGS. 1 and 4, with the drive circuit beingelectrically connected to the three electromagnetic coils forsequentially energizing the three electromagnetic coils 50, 52, 54 toreciprocate the piston 24 within the tubular housing 12.

[0018] In a further invention, the piston 24 is provided with a sump.The piston 24 has a bearing 70 extending circumferentially around oneend of the piston 24, and another bearing 72 extending circumferentiallyaround the other end of the piston 24. The bearings 70, 72 are axiallyspaced apart along the piston 24, with the piston 24 having reduceddiameter, in relation to the diameter of the piston at the bearings 70,72, between the bearings 70, 72 to define a lubricating sump 74. Thesump 74 is of sufficient volume to hold a lubricating amount of oil, andin operation is at least partially filled with lubricating oil. As shownparticularly in FIG. 5, the bearings 70, 72 may be each sealed byO-rings, gaskets or other sealing elements (not shown) placed incircumferential grooves 76 between circumferential ribs 78. The oil inthe sump 74 lubricates the bearings 70, 72. The bearings 70, 72preferably fit with a close tolerance within the housing 12, beingseparated by a suitably small gap.

[0019] The linear engine 10 described here may act as a pump orcompressor. As a pump or compressor, the linear engine 10 may beconfigured one or more inlet and outlet valves 80, 82 respectively andcontrol mechanisms (conventional and not shown) to actuate the valves sothat the tubular housing or cylinder 12 and its contained piston 24,when the piston is moved within the cylinder, perform the function of apump or a compressor. The linear engine 10 may also be fitted with a rodor drive shaft 84 as shown in FIG. 2 on the rotor (piston 24) to permitthe transmission of the rotor's linear motion into useful energy in theform of a driven flywheel, for instance, or drive gear or pulley.

[0020] The electromagnets 20, 22 fixed adjacent to the cylinder 12within which is deployed the cylindrical shaft or piston 24, for examplea permanent magnet may be energized by AC or DC current controlled by amaster on/off switch, through drive/control circuit 26, whose purposeand configuration is to control the induction of magnetic field(s) atthe electromagnets of suitable polarity, intensity, and duration.

[0021] The sump 74 provides an oil reservoir with suitable sealing andrefilling means to provide lubrication to the shaft (piston 24) withinthe electromagnet-containing barrel/cylinder 12 of the body of themechanism. The oil reservoir 74 may, but does not necessarily, provide adamper or an energy store or bumper for the cylinder as well asproviding lubricant, if desirable, by pressure-sealing the sump. Thismethod of lubrication provides for friction-reduction and some coolingto the cylinder 12 and shaft 24. A smaller diameter shaft could bedeployed within a different system of bearings suspended centered withinthe cylinder containing the electromagnets, where the lubricant wasprovided by a sump at one end of the cylinder, and suitably sealed fromsplashing or other loss.

[0022] There may be other features in such an exemplary motor, such asthe provision of bumpers or motion-limiting means to avoid having thepump piston or the shaft invade the pump cylinder or the oil reservoirin an unwanted way, which are not specifically described here, but wouldbe apparent to one skilled in the art.

[0023] A further liquid lubricant-filled sump 86 is defined by thegasket/ring around the linear motor's rotor which is slidingly sealedwithin the motor's stator. The piston 24 is preferably a circularcross-sectioned rotor deployed within a fitting cylinder which is theinternal cavity of the motor's stator(s)), configured such that therotor is piston-like and the stator is sleeve or cylinder-like to applyand control lubricant. The sump 86, if pressurized, may be relied uponas an improved replacement for the wearable springs used in prior artreciprocating linear motors to return the piston to its startingposition within a work cycle. However, the piston's return to start mayas well, in one embodiment, be accomplished by the deployment of twostators (one at each end of the cylinder within which the rotor isdeployed) each energized in a timed cycle to drive the piston/rotor fromone end to the other, in which case a return spring or pressured closedcylinder means would not be required.

[0024] Thus, the stator component, once suitably lubricated by thelubricant in the sump, provides a novel support and bearing means toorient the linearly moved rotor in the linear motor optimally within thechanging magnetic fields produced at the stator.

[0025] The stator is, in an exemplary embodiment, formed in three parts30, 32, 34 of substantially equal inner diameter thus forming onecontinuous cylinder 12 within which the rotor can fit and move, to forma two-electromagnet stator in cylindrical form into which a singlemagnetic field rotor in the shape of a tightly fitted piston is located,oriented and borne.

[0026] The outer parts of the stator are each formed of suitablematerial which when wound with electrically-conductive wire or similarcoils 20, 22 and when said coil has a direct electrical current passingthere through, will form a solenoid style of electromagnet. The magneticfield produced by said electromagnet acts upon the permanent magnetwhich is (or is a significant part of) the rotor, to move the rotorthrough the field along its axis as supported by the said stator'scylindrical inner cavity. The two electromagnetic parts of the statorare electrically and magnetically isolated from each other by a thirdmiddle part 34 which is not conductive of either power or magnetic flux,and which is mounted between the two magnetically active parts.

[0027] The rotor and stator thus form a piston and cylinder,respectively. At one end of the cylinder may be a sump within whichlubricant is placed, and the rotor is at that end fitted with a gasketor O-ring configured such that the rotor is sealed with the cylinder,keeping the lubricant within its sump. The sump may be sealed ifrequired to form a return mechanism for the rotor, but in an exemplarytwo-field stator system, may be open to atmospheric pressure but builtto contain the lubricant within its cavity.

[0028] The rotor's other end may be configured in a number of ways tobear a work load, such as (by example) to form a piston and cylinderwith suitable inlet and outlet valves to compress fluid or to pump fluidfrom inlet to outlet, or to evacuate an inlet to form partial vacuum, orsimilar loads; similarly, to that end of the rotor may be attached adrive shaft which can be operatively linked to an eccentric to convertthe rotor's linear motion to a rotating drive motion, for example to adrive shaft.

[0029] A number of these rotor/stator driven-piston/cylinder systems canbe inter-linked, for example ganged to a crank-shaft, suitably timed, toform a multi-cylinder motor.

[0030] The end plates may have any of various designs, for examplescrewed in cover caps. The coils may be made of copper wire. Thenon-magnetic sleeve 34 may be 2-3 cm or more in width.

[0031] In one embodiment, the non-magnetic sleeve 34 was 127 mm long, 44mm inside diameter, with the end portions inserted in the sleeves 30, 32each being 25.4 mm long and 4 mm thick, the central portion havingrespective thicknesses of 6 mm and 8 mm on either side of the flange 18.The corresponding piston had length 127 mm, with the bearings each being16 mm wide, the end ribs being 4 mm wide and the other ribs and grooveseach being 3 mm wide. The grooves were 3 mm deep and the sump 74 was 9mm deep. The sleeves 30, 32 were 50.8 mm wide, with smaller ID 44.5 mm,and larger 52.5 mm, the OD being 56.5 mm. The length of the piston maybe varied, and could be 152.4 mm long for example in a housing havingoverall width of 177.8 mm. Width here refers to the axial direction,rather than radial. The housing may have an axial width to diameterratio of between 2 and 3. The sleeve radial thickness may be for examplefrom 1 mm to any suitable thickness, depending on the application. Evenif the sleeve is only as thick as a film, it is believed that usefulproperties are obtained.

[0032] As shown in FIGS. 6A, 6B and 6C, the linear engine may use apiston 24A that is hollow at both ends, a piston 24B that is solid or apiston 24C that is hollow at one end. The piston can be hollow in themiddle as well, and therefore provide a conduit from one end of thepiston to the other.

[0033] As shown in FIG. 7A, a housing or enclosed sleeve 12A may beformed with axially alternating non-magnetic sections 90, for examplemade of ceramic, corresponding to regions of no-flux (or low flux), andmagnetic sections 92 corresponding to regions of higher flux density,each fitted to an adjoining section with an annular tongue and groovedesign 91. The sections 90, 92, may be of any suitable width and radialthickness, providing there are alternating magnetic and non-magneticsections. The non-magnetic sections 90 may be made of ceramic. Thesleeve 12A may be used in a linear engine with a piston of the typeshown in FIG. 1, with multiple coils, each coil being placed over acorresponding magnetic section 92 as illustrated in FIG. 1.

[0034] As shown in FIG. 7B, a sleeve 12B may be formed withcirumferentially alternating magnetic strips 94 and non-magnetic strips96, for example made of ceramic, each fitted to adjoining strips with atongue and groove design 95. The strips 94, 96, may be of any width,providing there are alternating magnetic and non-magnetic sections. Themagnetic sections 92 and strips 94 correspond to regions of higher fluxdensity. The enclosed sleeve 12B is used with a series of coils spacedaround the sleeve 12B in conventional fashion with a conventional rotorinside. Apart from the sleeve 12B, the motor this produced isconventional, with conventional coils, power supply, bearings, bushingsand rotor. The enclosed sleeve 12B is used with a series of coils spacedaround the outside of the sleeve 12B in conventional fashion with aconventional rotor or stator inside.

[0035] It is believed that the no or low flux non-magnetic sectionsdisclosed here help protect the coils from damage, for example fromburning out. An important advantage of the design disclosed here is thatit provides an integral sleeve with an integrated flux and no-fluxpattern corresponding to the alternating magnetic (flux) andnon-magnetic (no-flux) sections.

[0036] There are a number of methods of controlling the electricallycurrent flow, duration, direction, and power characteristics, responsiveto the motor's operating characteristics, its design characteristics,the load or desired power production, power available, or other means,and may be done electro-mechanically, by computational means, responsiveto sensors, or self-regulating through feedback mechanisms.

[0037] The invention has particular application (but is not therebylimited) in the field of provision of small-volume, quiet, compressorsfor refrigeration and similar equipment. Larger scaled versions could beutilized as motive power for vehicles or heavier equipment, whereefficiency, long-life, quietness and reliability are important.

[0038] The housing 12 may be arranged in a circle, in which case thepiston will move around the circle, either continuously or byreciprocating within the housing. The linear engine of the presentinvention may be operated as a pump, compressor, motor or generator.

[0039] Although it is preferred that the sleeve be enclosed andcontinuous, there may be holes in the sleeves, providing the holes allowalternating patterns of high flux and low flux with magnetic sectionsseparated by non-magnetic sections. The coils may have less or moreaxial width (along the tubular sleeve) than the magnetic section,depending on the application, but it is preferred that the coils havethe same width as the magnetic sections of the sleeve. The non-magneticsection of the sleeve only allows the coils to be separated so that theyare not one coil. The lower the magnetic flux between the magneticsections, the better, with preferably zero flux, as for example may beobtained if the nonmagnetic material is superconducting.

[0040] Immaterial modifications may be made to the invention describedhere without departing from the essence of the invention.

What is claimed is:
 1. An engine, comprising: a tubular housing; a firstelectromagnetic coil disposed around the tubular housing; a secondelectromagnetic coil disposed around the tubular housing and axiallyspaced from the first electromagnetic coil along the tubular housing; apiston disposed within the tubular housing, the piston includingmagnetic elements; a drive circuit electrically connected to the firstand second electromagnetic coils for sequentially energizing the firstand second electromagnetic coils to move the piston within the tubularhousing; a first magnetic sleeve disposed inside the firstelectromagnetic coil, the piston being arranged to pass through thefirst magnetic sleeve during operation; a second magnetic sleevedisposed inside the second electromagnetic coil, the piston beingarranged to pass through the second magnetic sleeve during operation;and the first magnetic sleeve being separated from the second magneticsleeve by nonmagnetic material.
 2. The engine of claim 1 in which thefirst magnetic sleeve and the second magnetic sleeve each form part ofthe tubular housing.
 3. The engine of claim 1 further comprising: athird electromagnetic coil disposed around the tubular housing andaxially spaced from the second electromagnetic coil along the tubularhousing; the drive circuit being electrically connected to the thirdelectromagnetic coil for sequentially energizing the first, second andthird electromagnetic coils to move the piston within the tubularhousing; a third magnetic sleeve disposed inside the thirdelectromagnetic coil, the piston being arranged to pass through thethird magnetic sleeve during operation; and the third magnetic sleevebeing separated from the second magnetic sleeve by non-magneticmaterial.
 4. An engine, comprising: a tubular housing; a firstelectromagnetic coil disposed around the tubular housing; a secondelectromagnetic coil disposed around the tubular housing and axiallyspaced from the first electromagnetic coil along the tubular housing; apiston disposed within the tubular housing, the piston includingmagnetic elements; a drive circuit electrically connected to the firstand second electromagnetic coils for sequentially energizing the firstand second electromagnetic coils to move the piston within the tubularhousing; and the piston having a first bearing extendingcircumferentially around the piston, and a second bearing extendingcircumferentially around the piston, the first and second bearings beingaxially spaced apart along the piston, the piston having reduceddiameter, in relation to the diameter of the piston at the first bearingand at the second bearing, between the first bearing and second bearingto define a lubricating sump between the first bearing and the secondbearing.
 5. The engine of claim 4 further comprising: a first magneticsleeve disposed inside the first electromagnetic coil, the piston beingarranged to pass through the first magnetic sleeve during operation; asecond magnetic sleeve disposed inside the second electromagnetic coil,the piston being arranged to pass through the second magnetic sleeveduring operation; and the first magnetic sleeve being separated from thesecond magnetic sleeve by nonmagnetic material.
 6. The engine of claim 5in which the first magnetic sleeve and the second magnetic sleeve eachform part of the tubular housing.
 7. The engine of claim 5 furthercomprising: a third electromagnetic coil disposed around the tubularhousing and axially spaced from the second electromagnetic coil alongthe tubular housing; the drive circuit being electrically connected tothe third electromagnetic coil for sequentially energizing the first,second and third electromagnetic coils to move the piston within thetubular housing; a third magnetic sleeve disposed inside the thirdelectromagnetic coil, the piston being arranged to pass through thethird magnetic sleeve during operation; and the third magnetic sleevebeing separated from the second magnetic sleeve by non-magneticmaterial.
 8. The engine of claim 4 in which each of the first bearingand the second bearing comprise axially spaced circumferentiallyextending ribs, adjacent ribs being separated by a gap for receiving asealing element.
 9. An engine, comprising: a tubular housing, thetubular housing being formed from alternating sections of magneticmaterial and non-magnetic material; plural electromagnetic coilsdisposed around the exterior of the tubular housing, with eachelectromagnetic coil being placed over a corresponding section ofmagnetic material; a movable magnetic element disposed within thetubular housing; and a drive circuit electrically connected to theplural electromagnetic coils for sequentially energizing theelectromagnetic coils to move the movable magnetic element within thetubular housing.
 10. The engine of claim 9 in which the movable magneticelement is a piston arranged to reciprocate within the tubular housing.11. The engine of claim 9 in which the non-magnetic material is ceramic.12. The engine of claim 9 in which the magnetic material is steel. 13.The engine of claim 1 in which the non-magnetic material is ceramic. 14.The engine of claim 1 in which the magnetic material is steel.